[PATCH 11/13] virtio_balloon: unaccept free reporting ranges

[Kevin Loughlin <kevinloughlin@google.com>]

In confidential computing guests with dynamic unaccepted memory
transitions, configure the free page reporting order to
unaccepted_memory_order(). Invoke mark_memory_unaccepted() on each
scatterlist range in virtballoon_free_page_report() before adding the
scatterlist to reporting_vq and kicking the host.

Unaccepting the pages prior to virtqueue_add_inbuf() and virtqueue_kick()
guarantees that the guest finishes PVALIDATE(validate=false) before the
host VMM can observe the reporting request in the virtqueue ring and
punch a hole in guest_memfd, eliminating any race where the guest
re-allocates and re-accepts a page before a deferred host hole-punch
executes.

Signed-off-by: Kevin Loughlin <kevinloughlin@google.com>
---
 drivers/virtio/virtio_balloon.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index d162c162b496..e10bd792ef7c 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -213,7 +213,26 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i
 	struct virtio_balloon *vb =
 		container_of(pr_dev_info, struct virtio_balloon, pr_dev_info);
 	struct virtqueue *vq = vb->reporting_vq;
-	unsigned int unused, err;
+	unsigned int unused;
+	int err;
+
+	if (virtballoon_cc_needs_state_transition()) {
+		unsigned long unit_size = PAGE_SIZE << unaccepted_memory_order();
+		struct scatterlist *sgl;
+		unsigned int i;
+
+		for_each_sg(sg, sgl, nents, i) {
+			if (WARN_ON_ONCE(!IS_ALIGNED(sg_phys(sgl), unit_size) ||
+					 !IS_ALIGNED(sgl->length, unit_size)))
+				return -EINVAL;
+		}
+		for_each_sg(sg, sgl, nents, i) {
+			err = mark_memory_unaccepted(sg_phys(sgl), sgl->length);
+			if (err)
+				return err;
+			cond_resched();
+		}
+	}
 
 	/* We should always be able to add these buffers to an empty queue. */
 	err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT);
@@ -1142,8 +1161,11 @@ static int virtballoon_probe(struct virtio_device *vdev)
 		 * host's base page size. However, it needs more work to report
 		 * that value. The hard-coded order would be fine currently.
 		 */
+		if (virtballoon_cc_needs_state_transition())
+			vb->pr_dev_info.order = unaccepted_memory_order();
 #if defined(CONFIG_ARM64) && defined(CONFIG_ARM64_64K_PAGES)
-		vb->pr_dev_info.order = 5;
+		else
+			vb->pr_dev_info.order = 5;
 #endif
 
 		vb->pr_dev_info.capacity = capacity;
-- 
2.56.0.307.g5fe7bd680c-goog